Method for determining limits for controlling traffic in communication networks with access control

ABSTRACT

The invention relates to a method for determining limits for the access control of traffic that is to be transmitted via a communication network. The limits are fixed in such a way that no overload situation can occur in the network; the probability of rejection of traffic flows is, wherever possible, is independent from the point of entry into said network; and resources are used as efficiently as possible. On the basis of limits wherein no overload situation occurs, the limits for the traffic control are raised in such a way that the blocking probability for traffic transmitted between pairs of marginal modes is lowered at the same time. The lowereing of said blocking probability is maintained if an overload situation were to occur in the network. For pairs of marginal nodes contributing to the occurrence of an overload situation, the limits for traffic transmitted between the marginal nodes are fixed at a value prior to or during the overload situation, the limits for traffic transmitted between the marginal nodes are fixed at a value prior to or during the overload situation. The method can be continued for the other pairs until all limits have been set. The method results in efficient transmission of energy while maintaining quality of service parameters.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is the US National Stage of International ApplicationNo. PCT/EP2004/000213, filed Jan. 14, 2004 and claims the benefitthereof. The International Application claims the benefits of Germanapplication No. 10301966.9, filed Jan. 20, 2003, both applications areincorporated by reference herein in their entirety.

FIELD OF INVENTION

The invention relates to a method for a balanced determination of valuesfor limiting traffic in a communication network with access controls,with the communication network being formed by nodes and connectionlinks and with access being controlled by means of a limit value for atleast a part of the traffic which is to be transmitted between marginalnodes over the network.

SUMMARY OF THE INVENTION

The control or limiting of the traffic—both data traffic and voicetraffic—is a central problem for communication networks which useconnectionless operation where traffic is to be transmitted with highquality-of-service requirements, such as voice data transmission forexample. Suitable mechanisms for checking the traffic are currentlybeing investigated by network specialists, telecommunications engineersand Internet experts.

Possibly the most important current development in the network area isthe convergence of voice and data networks In the future transmissionservices with a very wide diversity of requirements will be transmittedover the same network. The feature which marks out such developments isthat a large part of the communication over networks in the future willbe via networks which operate in connectionless mode, the most importantrepresentative of which is what is known as the IP (IP: InternetProtocol) network. The transmission of what is referred to as realtimetraffic, e.g. voice or video data over data networks while preservingquality-of-service features is the prerequisite for successful networkconvergence. For the transmission of realtime traffic over data networksin particular narrow limits have to be adhered to as regards delay timesand the packet loss rate of data packets.

One possibility for transmission in real time over data networks whilemaintaining quality-of-service features is to switch a connectionthrough the entire network, i.e. to define and reserve in advance theoperating means or resources required for the service. The provision ofsufficient resources to guarantee the service features is then monitoredfor each connection section (also known as a “link”). Technologies whichoperate in this way are for example ATM (ATM: Asynchronous TransferMethod) or the MPLS (MPLS: Multiprotocol Label Switching) protocol whichprovides for the definition of paths through IP networks. Thedisadvantage of these methods however is their great complexity and—incomparison to conventional data networks—lower flexibility Statusinformation about the flows switched through the network must be storedor checked for the individual links.

A method which avoids the complexity of link-by-link checking or controlof resources is what is known as the Diff-Serv concept. This concept isreferred to as “stateless” to indicate that no status information aboutdata connections or flows along the transmission path has to bemaintained. Despite this the Diff-Serv concept only provides for accesscontrol at the margins of the network. With this access control packetscan be delayed in accordance with their service features, and—ifnecessary—discarded. This is also described as traffic conditioning orpolicing, traffic shaping and traffic engineering. The Diff-Serv conceptthus allows a distinction to be made between different trafficclasses—frequently called classes of service—which can be prioritized inaccordance with the transmission requirements and/or handled with alower priority. Lastly with data transmission with the aid of theDiff-Serv concept it is not possible to guarantee that service featuresare maintained for realtime traffic. There are no mechanisms availableto adapt the realtime traffic transmitted over the network so thatreliable statements about the maintenance of the service features wouldbe possible.

It is thus desirable for the control of the realtime traffic transmittedover the data network to be good enough that on the one hand servicefeatures can be guaranteed and on the other hand optimum use is made ofresources, without having to take account of the complexity ofconnections switched through the network.

The object of the invention is to specify an optimized method for thedefinition of limit values for traffic restriction in a communicationnetwork.

The object is achieved by the claims.

In accordance with the invention limit values are defined for limitingtraffic in a communication network (e.g. an IP network). For datatransmission over the communication network there is provision foraccess control to be undertaken for at least a part of the traffic to betransmitted—e.g. for one or more classes of service before resources ofthe network are used for transmission. Access is controlled in this caseat marginal nodes of the communication network formed by nodes andlinks. A marginal node in this case can be a network access node (alsoknown as an ingress node) or a network output node (also known as anegress node), as well as an end or start note of a data transmissionlocated in the communication network, i.e. a node of the network whichrepresents a source or sink as regards the traffic. In the latter casethe term “marginal” in the word marginal node does not refer to thenetwork but to the transmission path of data packets.

The starting point for the invention is the consideration that balancedtraffic handling which is subject to access control, before networkresources are made available for the traffic, is present if thelikelihood of a non-approval or rejection of the traffic is asindependent as possible from the marginal nodes (e.g. ingress nodes andegress nodes) or the transmission path. The invention will look at aplurality of pairs formed by the marginal nodes. A pair of marginalnodes can be associated with the set of possible paths leading throughthe network which run between the two marginal nodes. With the pairs ofmarginal nodes the sequence of the marginal nodes is taken into account,i.e. two marginal nodes can define two different pairs depending on howthe sequence of the two marginal nodes is looked at. In other words, forassociation of different paths with pairs of marginal nodes the pathsare assigned a direction or a direction sense. Pairs of marginal nodescan for example consist of a an ingress node and an egress node, of aningress node and a network node which can be receiver or addressee oftransmitted data, as well as a network node which functions as atransmitter, and an egress node.

The probability of non-approval of traffic or of flows which are subjectto an approval check at an marginal node can be estimated using trafficmodels. The invention starts from the assumption that with the aid of atraffic model the probability of rejection of traffic—referred to belowas blocking probability—will be determined. This type of traffic modeltypically delivers values for the average traffic intensity between twomarginal nodes and specifies a relationship for taking the trafficfluctuations into account. For example it can be assumed that trafficfluctuations belong to a Poisson distribution with which the probability(in our case the blocking probability) of the limit value for the accesscontrol being exceeded can be estimated. The blocking probabilities andthe limit values for access control are interrelated and can generallybe converted into one another. With the method in accordance with theinvention, for plurality of pairs formed from marginal nodes, theinitialization step consists of setting the blocking probabilities bydefining the limit values for the access control so that they areessentially the same. The initial blocking probabilities here are chosenso that they are big enough for no overload situations to occur in thenetwork. This definition corresponds to fair handling of the data streamtransmitted between the marginal nodes, to the extent that there ispractically the same probability of it being allowed or rejected. Withthis definition however there is as yet no guarantee that the resourcesavailable to the network will be used efficiently. As regards efficientresource utilization, the method in accordance with the invention makesprovision for lowering the blocking probability, i.e. increasing thelimit values for access control correspondingly until an overloadsituation occurs. The lowering of the blocking probabilities or theincreasing of the limit values for the approval checking is undertakensuch that the blocking probabilities remain essentially the same for thepair of marginal nodes. For the pairs of marginal nodes involved whenthe overload situation arises, the blocking probabilities areessentially set to the value at which the overload situation would becaused by raising the limit values. For example the blockingprobabilities are lowered step-by-step and the value of the blockingprobabilities and thereby also the value of the corresponding limits isthen set for the pairs contributing to the overload situation to thevalue that it had in the step directly before the overload situationoccurred.

The advantage of the invention is that in a network without explicitpath reservation limits can be defined for access control in a balancedand resource-efficient way. In accordance with a development of theinvention limit values are defined for all pairs of the plurality ofpairs formed from marginal nodes. In this case, for pairs which were notinvolved in the occurrence of the first overload situation, the blockingprobability is further lowered simultaneously for all remaining pairsuntil a second overload situation occurs. For the pairs involved in theoccurrence of the overload situation the blocking probabilities or thelimit values are essentially frozen or maintained at the value whichthey had on occurrence or shortly before the occurrence of the overloadsituation. This step is then repeated until such time as limit valueshave been defined for all pairs i.e. the blocking probability issimultaneously increased for the remaining pairs until an overloadsituation occurs in which, for the pairs involved in the overloadsituation, the blocking probability is retained until such time as theblocking probability is in place for all pairs.

With this development there are two points to note:

1. The development leads to an assignment of blocking probabilities orlimit values for all pairs since a blocking probability of zero for apair would mean that one would be able to transmit an unlimited amountof traffic between the edge points of the pair without any overloadsituation arising, which is evidently not the case for real networks.

2. The blocking probability or limit values for all pairs of theplurality of pairs is defined so that a lowering of the blockingprobability of any given pair from the plurality would lead to anoverload situation. In this sense an optimum utilization of theresources available to the network is produced.

The plurality of pairs includes for example all pairs of ingress nodesand egress nodes. In this case complete control of the traffic enteringthe network and leaving the network again is provided, or of the trafficof the class of service which is subject to access control. The settingof the limits or the choice of the blocking probabilities guaranteesthat no overload situation occurs; As a consequence definitivestatements can be made about the quality-of-service features. Thesetting of limits for access control then opens up the possibility ofquality of service with simultaneously a best possible utilization ofthe resources available.

Communication networks have physical restrictions for the transmissioncapacity over the connection sections or links which are enclosed by thenetwork. The maximum transmission capacity of the individual linksdefines an upper limit for the traffic able to be transmitted over thelink in question. Frequently limits on the traffic volume over theindividual links are set lower than the maximum physical capacity inorder to provide spare capacity on the one hand and on the other hand toprevent faults occurring in the network. In the latter case the focus isfrequently on the resilience of a network, i.e. the capability ofensuring problem-free transmission even with failures of networkelements. For the communication network discussed above the limits forthe traffic on the individual links can for example be selected so thatthe failure of one (or more) links does not lead to the physical limitsfor the capacity of the other links being exceeded, i.e. even if a linkfails the traffic which was subject to access control can be managed. Anoverload situation in the sense of the method in accordance with theinvention can then be defined as the fact that the defined limits forthe traffic volume on this link could have been exceeded on a connectionsection or a link of the network. Checking the communication network forthe possibility of an overload situation can be undertaken for examplewith the aid of a model for the load distribution within the network. Acheck is made for example using a simulation program as to whether thereare links in the communication network for which a maximum traffic loadwithin the framework of the defined limits would lead to the permittedtraffic volume for the link being exceeded. Another slightly modifieddefinition would be that the limits covering volume of traffic on theindividual links would be likely to be exceeded with high predefinableprobability. The pairs of marginal nodes which contribute to an overloadsituation produced by a limit value being exceeded for the traffic on alink would then be those to which paths could be assigned which run viathe link which is causing the overload situation. In traffic theory theterm traffic pattern is usually used to designate the real(instantaneous) traffic present at the inputs of the network. Checkingfor an overload situation can then be undertaken by checking whether thetraffic pattern allowed by the limits, taking into account the routingsundertaken in the network, would then lead to an overload situation ornot.

The object of the invention is explained in more detail below within thecontext of an exemplary embodiment which refers to a FIGURE.

BRIEF DESCRIPTION OF THE DRAWING

The sole FIGURE shows a network made up of nodes and links.

DETAILED DESCRIPTION OF THE INVENTION

The FIGURE shows a network made up of nodes and links. In this case themarginal nodes R1 to R10 are indicated by solid circles. The internalnodes are indicated by non-solid circles. Links are illustrated byconnectors between nodes. For the network different types of peripheralconditions can be defined which guarantee approval control at the marginof the network. The type of peripheral conditions can for example beselected to depend on the topology of the network. The form of theperipheral conditions helps to decide on the blocking probabilities forwhich an overload situation occurs in accordance with the inventivemethod. Possible peripheral conditions are:

-   -   1. Limits for the traffic which is transmitted between two        marginal nodes, i.e. a limit value in each case for a pair        (Ri,Rj), j, i ε{1, . . . , 10}, which is defined by two marginal        nodes.

2. Limit values for all ingress and egress nodes. If we assume that allmarginal nodes Ri, i ε{1, . . . , 10} are both ingress and egress nodes,this would produce 20 limit values, with two limit values, an ingressvalue and an egress value being assigned to a node in each case. For aflow which is to be transmitted from the ingress node Ri to the egressnode Rj a check would then be made on whether the node would exceed theingress limit for Ri or the egress limit for Rj. Exceeding the limitwould result in rejection.

3. Ingress and egress limit values as for Point 2. but for all links ofthe network. This means that for each link L one has two limits permarginal node in each case. For the transmission of a flow from node Rito node Rj the ingress limits of Ri and the egress limits of Rj would bechecked which relate to links over which the flow is to be transmitted.

To simplify matters the explanation belows assumes the form of limitsdescribed in 1. above. They are to form the basis of a traffic modelwhich allows an average volume of traffic between two marginal nodes Riand Rj to be determined. The average traffic between two marginal nodesRi and Rj is designated for simplicity's sake as Vij. Likewise Gij istaken as the limit value for the traffic transmitted from the ingressnode Ri to the egress node Rj. A flow to be transmitted from Ri to Rj isallowed if the aggregated traffic between Ri and Rj would not exceed thelimit Gij. In this case j,i ε {1, . . . , 10} always applies. Thetraffic model uses the average traffic values Vij and assumptions aboutthe statistical fluctuations, which belong to a Poisson distribution forexample. To initialize the method the limit values Gij are set so (low)that the same blocking probabilities exist for all pairs (Ri,Rj) andthat in addition no overload situation occurs. Checking for theoccurrence of an overload situation can be undertaken for example bydetermining, for the maximum traffic load allowed by the limit valueswith the inclusion of the routings within the network, the traffic loadof the individual links and comparing this with the limits or capacityof the links. In accordance with the invention the blockingprobabilities are lowered by the same percentage ratio and the limitvalues Gij correspondingly increased. In this case, with the aid or thetraffic model, for a set of reduced, similar values of the blockingprobability a corresponding set of limit values Gij (analytical ornumerical) is determined, which—within the framework of the trafficmodel—defines a non-approval with the reduced blocking probability forall pairs (Ri,Rj). A check for overload follows. If no overload occursthe blocking probability is further lowered simultaneously for allcommunication links. This can for example occur through step-by-steplowering by 10 of the initial value. In one step, for example the fiftha bottleneck or an overload situation occurs on the link L, i.e. thelimits for the capacity on this link would be exceeded by the choice oflimits at step 5. The pairs (R1,R2), (R2,R1), (R1,R3), (R3,R1), (R1,R4)and (R4,R1) contribute to this overload situation for example. For thesepairs the limits Gij or the blocking probability are then set to theirvalue at step 4. The method is then continued for the remaining pairs(Ri,Rj) until limits Gij are defined for all pairs (Ri,Rj).

1-10. (canceled)
 11. A method for setting limit values of an accesscontrol for limiting traffic transmission in a communication network,wherein the communication network comprises a plurality of pairs ofmarginal nodes between which the transmission occurs, and the limitvalues of the access control are limit values regarding the pairs, themethod comprising the following steps: setting the limit values suchthat probabilities for each of the pairs related to not approving thetransmission between the marginal nodes of the pair are substantiallythe same, and such that an overload situation in the communicationnetwork does not occur; increasing the limit values to a minimum valueat which an overload situation starts to occur, such that theprobabilities are substantially the same; and updating the limit valueregarding at least one of the pairs of marginal nodes, between which atransmission occurs causing the overload situation, by setting the limitvalue to the minimum value.
 12. The method in accordance with claim 11,wherein the probabilities related to not approving the transmissionbetween the marginal nodes of the pairs are blocking probabilitiesrelated to blocking the transmission between the marginal nodes of thepairs.
 13. The method in accordance with claim 11, wherein the marginalnodes include nodes of the network representing sources or sinks oftraffic of the network.
 14. The method in accordance with claim 11,wherein the marginal nodes are specified by ingress nodes and egressnodes of the network.
 15. The method in accordance with claim 14,wherein the plurality of the pairs comprises all pairs of the networkconsisting of an ingress node and an egress node in each case.
 16. Themethod in accordance with claim 11, wherein the overload situation isproduced when in a scenario of high traffic load, in which the limitvalues for the access controls are still adhered to, a threshold valueis exceeded on a link for the traffic transmitted over the link.
 17. Themethod according to claim 16, wherein the threshold value for thetraffic transmitted over the link is assigned to the link such that incase of failure of the link, the traffic allowed within the framework ofthe access controls does not represent any overload.
 18. The method inaccordance with claim 11, further comprising: further increasing thelimit values regarding further pairs of the pairs, which for the limitvalue is not determined yet, in excess of the minimum value to a furtherminimum value at which a further overload situation starts to occur,such that the probabilities are substantially the same; and updating thelimit value regarding at least one of the further pairs of marginalnodes, between which a transmission occurs causing the further overloadsituation, by setting the limit value to the further minimum value. 19.The method in accordance with claim 18, comprising repeating the furthersteps until the limit values for all of the pairs are determined. 20.The method in accordance with claim 18, wherein the further overloadsituation is produced when in a further scenario of high traffic load,in which the limit values for the access controls are still adhered to,a further threshold value is exceeded on a further link for the furthertraffic transmitted over the further link.
 21. The method according toclaim 20, wherein the further threshold value for the further traffictransmitted over the further link is assigned to the further link suchthat in case of failure of the further link, the further traffic allowedwithin the framework of the access controls does not represent anyoverload.
 22. The method in accordance with claim 11, furthercomprising: making access checks for all the traffic of a class ofservice.
 23. The method in accordance with claim 22, wherein the accesschecks relate to an approval or rejection of individual flows.
 24. Anetwork node with means for executing the method in accordance withclaims
 11. 25. The network node according claim 24, wherein the networknode is a marginal node of the network.